In the semiconductor manufacturing fields, the motive for developing high density semiconductor devices, i.e.. ICs of over the VLSI scale lies in the fact that the price per IC unit can be lowered by increasing the chip density. In this connection, the structure of transistors and the design of cells have been developed to reduce the occupied area for a basic cell.
For example, in designing the cells of RAM (random access memory) in which writing and reading of data are possible, the structure of the cell has been advanced from a dynamic 4-transistor cell derived from a flip-flop circuit, via a 3-transistor cell sharing the feedback paths between cells, to a 1-transistor cell consisting of a single MOS transistor and a single capacitor for storing charges.
However, in the process of increasing the density by reducing the occupied area of the basic cell or by simplifying the structure for the basic cell which constitutes a certain function block, various problems have been produced due to the very simplicity of the structure. For example, in the case of a RAM consisting of 1-transistor cells, the gate capacitance itself is not enough for the storage capacitor.
For this reason, there is the hazard that the stored data can be damaged when reading out the data, and further, a highly sensitive amplifier is needed because of extreme weakness of the output voltage (Refer to "Storage Array and Sense/Refresh Circuit for Single Transistor Memory Cells" by Stein, K.U. et al., IEEE Journal of Solid State Circuits, SC-7, No. 5, pp. 336-40).
However, even if an amplifier capable of amplifying the extreme weak voltage with a high amplifying ratio is provided, and further if the amplifier consists of a static amplifier, when an external noise intrudes upon the output of the cell, then the static amplifier will amplify the deformed cell output including the external noise, with the result that undesirable signals will be continuously outputted.